1. Field of the Invention
The present invention relates to a probe of a scanning probe microscope (SPM), having a tip formed as a field effect transistor (FET) channel, and a method of fabricating the same.
2. Description of the Related Art
Various kinds of microscopes capable of measuring different types of physical quantities by scanning with a probe are referred to as scanning probe microscopes (SPMs).
An SPM basically includes a probe with a sharp tip (having a radius of curvature of 10 nm or less, a scanner for scanning a sample with the probe, and a control and information process system for controlling the probe and scanner and processing signals. A variety of different types of SPMs have been developed. The operation principle of the probe varies depending on the physical quantity to be measured. Different types of SPMs include a scanning tunneling microscope using a current flow due to voltage difference between the tip and the sample, an atomic force microscope using various types of atomic forces existing between the tip and the sample, a magnetic force microscope using a force exerted between the magnetic field of the sample and the magnified tip, a scanning near-field optical microscope whose resolution limit to visible wavelength is improved, and an electrostatic force microscope (EFM) using electrostatic force acting between the sample and the tip. A variety of different types of tips are available for measuring a variety of samples with great precision. With the SPMs based on the variety of operation principles, which are initially devised for the purpose of topology measurement, physical characteristics such as the friction coefficient, thermal conductivity, magnetic domain, ferroelectric domain, electric potential difference, and electrochemical characteristic, as well as the topology characteristic, can be measured with great precision.
FIG. 1 is a schematic view of a disc apparatus using a conventional SPM probe. The disc-type recording/reproduction apparatus using the SPM probe includes a disc 8 having a circular substrate, an electrode layer deposited on the substrate, and a ferroelectric layer deposited on the electrode layer; a head 9 having a microtip for recording information onto the ferroelectric layer by dielectric polarization and reading information therefrom while vertically moving within the range of xcex/4 (xcex is light wavelength over the disc surface depending on the polarities, and a light beam reflecting means; and an optical system 100 for detecting the recorded information from the optical path difference by the vertical movement of the head 9.
In particular, referring to FIG. 1, the electrode layer 8b, and the ferroelectric layer 8c on which information is recorded by dielectric polarization are sequentially stacked on the circular substrate 8a of the disc 8. The head 8 formed as an SPM probe includes the microtip 9a for directly recording information on the ferroelectric layer 8a by dielectric polarization, and reading information from the ferroelectric layer 8a while vertically moving within the range of xcex/4 over the disc surface depending on the polarities, the reflector 9b for reflecting a light beam, and a support arm 9c for supporting the microtip 9a and the reflector 9b. The optical system 100 includes a laser diode 1 as a light source, a collimating lens 2 for collimating the light beam emitted from the light source 1, a beam splitter 3 for passing the parallel light beam and splitting a light beam reflected from the disc surface; an objective lens 5 for focusing the incident parallel beam on a track of the disc surface to a diffraction limit, a condensing lens 6 for condensing a reflected beam, and a photodetector 7 for converting the condensed reflected beam into an electric signal.
The operational principle of the disc apparatus having the configuration described above is as follows.
As a small region of the ferroelectric layer deposited on an electrode plate is polarized by moving the microtip electrode to which a constant voltage is applied, a polarized region, and a non-polarized region or inversely polarized region can be distinguished from the difference in electrostatic force therebetween. An electrostatic force is exerted upon the microtip of the head to which a constant voltage is applied, which varies depending on the intensity of polarization of the disc surface, and the microtip rises or falls by an amount of xcex/4 or less. Here, only a light beam with an optical path variation of xcex/2 is split by the beam splitter 3 and is detected by the photodetector 7.
FIG. 2 is a schematic view of a morphology measuring apparatus using a conventional SPM probe. As shown in FIG. 2, as a cantilever probe 19 oscillates by a piezoelectric device 20 and a sample 21 is moved by an x-y-z scanner 22 controlled by a controller 25, a sharp tip 19a of the cantilever probe 19 scans the surface of the sample 20. Thus, the body of the cantilever probe 19 also moves up and down depending on the surface shape of the sample 20 and reflects the laser beam emitted from a laser source 23 towards a photodetector 24. The intensity of the reflected beam is detected as an electric signal to display the morphology of the sample 20 on a display 27.
As described previously, in the SPM technique of measuring a force acting between the probe and an object to be measured with mechanical devices and a laser diode, the probe tip needs to be positioned as close as possible to the object and to be extremely sharp. This SPM technique is affected by the surface flatness of a substrate used, so that it has a controlling problem. The large volume of the entire system is defective in manufacturing a miniature hard disc.
To solve the problems, it is a first object of the present invention to provide a probe of a scanning probe microscope (SPM) having a field-effect transistor (FET) channel with simple configuration, which can easily measure a force acting between a probe tip and a sample in connection with peripheral devices.
It is a second object of the present invention to provide a method of fabricating the SPM probe.
To achieve the first object of the present invention, there is provided a probe of a scanning probe microscope, having a field-effect transistor channel structure and comprising: a tip; a channel region formed by doping a center sloping portion of the tip with a first type of impurities; and a source region and a drain region formed at the sloping sides of the tip around the channel region by doping the sloping sides with a second type of impurities.
In an aspect of the second object of the present invention, there is provided a method of fabricating a probe of a scanning probe microscope having a field-effect transistor channel, the method comprising: (a) forming a tip by etching a single crystalline semiconductor substrate along a crystalline surface; (b) forming a channel region by doping a center sloping portion of the tip with a first type of impurities; and (c) forming a source region and a drain region by doping the sloping sides of the tip with a second type of impurities. It is preferable that, in step (a), a single crystalline semiconductor substrate having the (100) plane is used and is etched such that the (111) planes are exposed at the sloping sides in which the source region and drain region are to be formed.
In another aspect of the second object of the present invention, there is provided a method of fabricating a probe of a scanning prove microscope having a field-effect transistor channel, the method comprising: forming a tip by etching a single crystalline semiconductor substrate along the (100) plane, such that one end of the V-shaped groove to be a tip has a first angle and the (111) plane is exposed at the sloping sides of the V-shaped groove; forming a source region and a drain region by doping the sloping sides of the V-shaped groove with a first type of impurities; etching only a center portion of the V-shaped groove at which the sloping sides having the source and drain regions doped with the first type of impurities meet to have a second angle greater than the first angle, and to remove the first type of impurities such that a channel doped with a second type of impurities is formed at the center portion of the V-shaped groove. It is preferable that the first angle is 90 degrees and the second angle is 136 degrees.